Well, since your game is very much like Xiangqi as far as confinement is concerned, you could simply copy the BadZone and Shade routines from the mentioned Xiangqi page. And then adapt the tests on the file and rank coordinates x and y to your different board size. And the piece numbers of the pieces to be confined to the numbers they have in your piece table.
You could even start by copying them 'as is'. But you will see (if you specify different lightShade and darkShade) that the Palace will then not be in the location you want it, and that it might confine other pieces than you would want to be confined. You can then experiment a bit with the numbers in the routines that specify the Palace boundaries or piece types until you get what you want.
Well, since your game is very much like Xiangqi as far as confinement is concerned, you could simply copy the BadZone and Shade routines from the mentioned Xiangqi page. And then adapt the tests on the file and rank coordinates x and y to your different board size. And the piece numbers of the pieces to be confined to the numbers they have in your piece table.
You could even start by copying them 'as is'. But you will see (if you specify different lightShade and darkShade) that the Palace will then not be in the location you want it, and that it might confine other pieces than you would want to be confined. You can then experiment a bit with the numbers in the routines that specify the Palace boundaries or piece types until you get what you want.